This invention relates to a swing mechanism for the boom of an earth-moving apparatus such as a backhoe which includes an implement such as a bucket or other tool associated with the remote end of the dipper.
The swing mechanism includes a main frame which is attached to a fixed mount or to a vehicle such as a tractor. The bucket or other implement to be manipulated is connected to a dipper which is carried on the boom which, in turn, is carried on a swing frame. The swing frame is pivotally connected to the main frame for swinging about a vertical axis from one side of the main frame to the opposite side through an angle of approximately 200.degree. or more. The swing frame is conventionally powered by hydraulic actuating means acting through flexible means such as chains or cables. Some of the earlier swing mechanisms are powered by two ram type hydraulic actuators. One end of a flexible means such as a chain is attached to one end of the hydraulic actuator and the other end of the chain is attached to the swing frame. Another chain is attached to the other hydraulic actuator and the other end of the chain is also attached to the swing frame. One of the hydraulic actuators causes one of the chains to rotate the swing frame in one direction while the other hydraulic actuator retains the tautness of the chain in the other direction and vice versa.
Later improvements in the actuating means for the swing mechanism included replacing the two hydraulic actuators with a single double-acting hydraulic actuator. The driving connection between the hydraulic actuator and the swing frame includes a pair of elongated flexible connectors such as chains or cables. One end of each of the connectors is attached to the swing frame. The other end of each connector is attached to the portion of the hydraulic actuator which has a cylindrical bore. Rectilinear movement of the portion of the hydraulic actuator which has the cylindrical bore causes the swing frame to swing about a vertical pivot means. Such a device is shown in my U.S. Pat. No. 3,891,104.
Another similar swing mechanism for a boom is shown in U.S. Pat. No. 4,003,484 to Jones et al. The drive in this patent also includes a single hydraulic actuator and an elongated flexible connecting means such as a chain. The cylinder portion of the hydraulic actuator is pivotally attached at one end to the main frame. The piston portion of the hydraulic actuator is pivotally connected to a bar for lateral movement relative to the front to back axis of the main frame. A shaft on the swing mechanism is journalled onto the frame and carries a pair of superimposed sprocket wheels that are partially wrapped in opposite directions by a pair of drive chains. The chains are anchored to opposite ends of a bar which is reciprocable transversely of the upright axis of the pivot shaft. The bar is coupled to the piston portion of the hydraulic actuator so that when the hydraulic actuator is actuated, the bar reciprocates to wrap one of the chains about its sprocket wheel while the other chain is unwrapped from its sprocket wheel for swinging the boom about its vertical axis. My U.S. Pat. No. 4,078,680 discloses a swing mechanism whereby the flexible connector or chain is connected at one end to a drum which is fixed to the boom and at its other end to one end of a lever. The opposite end of the lever is pivoted to the main frame. The piston portion of the hydraulic actuator is pivotally attached to an intermediate portion of the pivoted lever. The cylindrical portion of the hydraulic actuator is pivotally connected to the main frame. The chain, pivoted lever and hydraulic actuator are utilized to swing the boom to one side of the tractor. A chain, pivoted lever and hydraulic actuator is utilized to swing the boom to the opposite side of the tractor.
One of the major disadvantages which is inherent in prior art swing mechanisms which utilize a flexible connector such as a chain is that the mechanism begins to lose its precision of movement as the chain begins to wear. The chains wear due to the hard and continuous use through which these machines are subjected to, the operator finds it increasingly difficult to locate the earth-moving member at a desired location. When the problem becomes acute enough, the chains must be manually adjusted. Proper tensioning is difficult to achieve. If the chains are over- tensioned, they are prone to break. If they are under- tensioned, the boom is hard to control because of looseness. Manually adjusting the tension of the chains is time-consuming, costly and impractical.
It is, therefore, a principal object of the invention to provide a hydraulically actuated swing mechanism for earth moving apparatus which includes a flexible connector, such as a chain and slide member, interposed between the swing frame and the actuator in which the mechanism automatically compensates for wear or stretching of the flexible connector.
Another object of the invention is to provide a swing mechanism as described above in which the flexible connector is a chain for which no sprockets are utilized.
A further object of the present invention is the provision of a swing mechanism for an earth moving apparatus in which each drive cylinder positively maintains a firm engagement between a slide member and guide means so that slop and play is eliminated thereby providing for a smoother acting mechanism and enabling the operator to have better control of the swing movement.
A still further object of the invention is the provision of a swing mechanism for an earth moving apparatus in which the guide means provides protection for the extended portions of the chain, to prevent digging debris from being packed into the chains which debris causes stretching, wear and failure of the chains.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.